The once monumental glaciers of Alaska are melting twice as fast today as they were 10 years ago, according to scientists who have measured the volume of ice that has disappeared over the past half century.

The once monumental glaciers of Alaska are melting twice as fast today as they were 10 years ago, according to scientists who have measured the volume of ice that has disappeared over the past half century.

Glaciologists, who have mapped more than 100 of Alaska's largest glaciers, believe that melting has increased dramatically since the early 1990s and that former mountains have become "molehills" since the 1950s.

Alaska's glaciers have been responsible for at least 9 per cent of the global sea-level rise over the past century, which is roughly equivalent to that caused by the melting of the massive Greenland ice sheet – a rise of 0.1mm each year.

Keith Echelmeyer and colleagues from the University of Alaska report in the journal Science that the glaciers mapped extend from the McCall glacier in the far north to the Salmon glacier in the south-east. "Most glaciers have thinned several hundred feet at low elevations in the last 40 years and about 60 feet at higher elevations," he said.

The scientists flew over the glaciers in aircraft mounted with a laser altimeter to measure the height of the peaks. Comparison with maps drawn 50 years ago revealed that 85 per cent of the glaciers measured lost vast volumes of ice up to the early 1990s. Comparison with data from identical flights during the early 1990s and in 2001 showed that thinning has doubled in a decade.

Columbia glacier in Prince William Sound has shrunk by an average of 24 feet a year and the Bering glacier in the St Elias Mountains has lost more than 10 feet of ice a year.

Dr Echelmeyer said it was not known if climate change was responsible.